Algebra problem involving standard notation & %.

Please help me solve these three problems:

The human body can produce 2.5 million blood cells per second. If a person donates 500mL of blood, how long will it take to replace the red blood cells if a litre of blood contains 5 * (10^12) red blood cells?

The Sun is approximately 1.5 * (10^8) km from Earth and a comet is approximately 3 * (10^6) km from Earth. How many times further from Earth than the comet is the Sun?

A music store sells three types of CDs: classical, blues and heavy metal. In one week the sold a total of 420 CDs. They sold 10% more classical than blues whiles sales of heavy metal constituted 50% more than the combined sales of classical and blues CDs. How many of each type of CD did they sell?

A music store sells three types of CDs: classical, blues and heavy metal. In one week the sold a total of 420 CDs. They sold 10% more classical than blues whiles sales of heavy metal constituted 50% more than the combined sales of classical and blues CDs. How many of each type of CD did they sell
Thanks in advance!

The human body can produce 2.5 million blood cells per second. If a person donates 500mL of blood, how long will it take to replace the red blood cells if a litre of blood contains 5 * (10^12) red blood cells?